1. Field of the Invention
This invention relates to an environment map building method and an environment map building apparatus for acquiring information within an environment and building an environment map and also to a mobile robot apparatus having a moving means such as legs and adapted to move, recognizing the obstacles within an environment where it is located.
2. Description of the Related Art
Unlike industrial robots, autonomous robot apparatus can autonomously act according to the external environment conditions of the surroundings and the internal conditions of the robot itself. Therefore, for example, autonomous robot apparatus are required to detect external obstacles and form a plan for its own moving route free from obstacles. Known robot apparatus include those that can build an obstacle map showing the obstacles in the environment where it is situated and decide its own moving route according to the built map.
Various studies have been and being made on algorithms for detecting a plane from the three-dimensional distance information that a mobile robot apparatus has acquired. The detected plane can be used, for example, by the mobile robot apparatus for avoiding obstacles and stepping up and down on staircases as well as for other purposes.
There has been proposed a technique of causing a robot apparatus to detect a plane from distance information, express the surrounding environment of the robot apparatus by means of a two-dimensional grid and move in the direction indicated by the linear sum of the repulsive force from all the detected obstacles and the attractive force relative to the target ([Patent Document 1]: U.S. Pat. No. 5,006,988).
According to another proposed technique, a robot apparatus that can estimate if there is an obstacle or not by detecting the floor surface by means of the distance information it acquires and identify the surrounding environment is realized by causing the robot apparatus to express the surrounding environment thereof by means of an environment map, which provides map information on a coordinate system centered at the robot apparatus, divide the environment into grid cells of a predetermined size so as to be able to hold the probability of existence of an obstacle in each grid of the map and treat each grid that shows a probability of existence exceeding a threshold value as an obstacle ([Patent Document 2]: Japanese Patent Application Laid-Open Publication No. 2003-269937). According to another technique achieved by developing the technique of the Patent Document 2, the two-dimensional grids are extended and the environment is expressed by means of a plurality of two-dimensional grids that are parallel to the horizontal plane. With this technique, planes of different heights are expressed by means of a plurality of two-dimensional grids.
There has been proposed another technique of acquiring three-dimensional information on the surrounding environment by surveying it by means of a stereovision and expressing the surrounding environment by means of three-dimensional grids (see, inter alia, [Non-Patent Document 1]: H. Moravec. “Robust Navigation by Probabilistic Volumetric Sensing”, DARPA MARS program research progress, 2002). According to still another technique, the surrounding environment of a robot apparatus is expressed by applying height information to each of two-dimensional grids by means of a 2.5-dimensional (2.5-D) height map that is drawn by assigning only an analog value of height information to each grid on the basis of three-dimensional information acquired by means of a stereovision (see, inter alia, [Non-Patent Document 2]: Kagami et al. (S. Kagami, K. Nishiwaki, J. J. Kuffner, K. Okada, M. Inaba, H. Inoue) Vision-based 2.5D terrain modeling for humanoid locomotion, Int. Conf. on Robotics and Automation (ICRA), 2003).